An implantable medical device (IMD) is an apparatus that is typically placed inside a living body to monitor certain physiological signals and provide therapy to an organ or tissue in response to the physiological signals. An example of an IMD is an implantable cardiac device (ICD) such as a pacemaker that stimulates the heart into a contraction if the sinus node is not properly pacing such contractions. Modern cardiac devices also perform many functions beyond that of pacing. For example, some ICDs perform defibrillation and cardioversion therapies. Other ICDs are able to select among several different pacing therapies depending upon the physiologic condition of a patient's heart.
A pacemaker device, as an example of an ICD, is typically implanted in a convenient location beneath a patient's skin and in the vicinity of one or more major arteries or veins. One or more electrical leads connected to the pacemaker are typically placed on or inside the patient's heart via a convenient artery or vein. The ends of the leads are placed in contact with the inside walls or the surface of one or more chambers of the heart, depending upon the particular therapies deemed appropriate for the patient.
One or more leads are adapted to carry a current from the pacemaker to the heart tissue to stimulate the heart in one of several ways, again depending upon the particular therapy being delivered. The leads are also used for sensing the physiologic signals provided by the heart to determine when to deliver a therapeutic pulse to the heart, and the nature of the pulse, e.g., a pacing pulse or a defibrillation shock. Further, one or more catheters may be connected to the IMD to deliver drugs to various body parts for pain relief, defibrillation threshold reduction, and so forth.
Distributing a variety of leads, catheters, and medical activators about a patient's body from a single IMD is a complex procedure. Further, many lead conductors and connections to the IMD are required in order for many electrodes to be distributed. Leads and connections are expensive and increase the overall IMD size. Further, as the number of leads extending from a central device increases, the overall system reliability is reduced.
Another type of IMD includes a plurality of leads for applying a pain therapy stimulus to various body areas such as the spinal column or the brain. For example, chronic pain originating in the lower back is a quite common ailment, and spinal cord stimulation is an accepted therapy for such pain. However, physicians have found that it can be difficult to properly position the spinal cord stimulation (SCS) lead to achieve good pain relief for lower back pain. Nerve fibers associated with lower back pain are only close to the dorsal column surface of the spinal cord for a short distance and are consequently difficult to locate. Physicians who consider properly treating lower back pain must develop an effective SCS technique and must learn to manipulate a stimulating lead with unusual skill and patience. Such a technique often involves implanting a stimulating device and carefully positioning at least one stimulating lead into a patient's spinal area. Even if the technique is performed properly, the leads may need to be repositioned over time. Repositioning the stimulating leads is typically an invasive surgical procedure that carries risks and requires great patience, care, and skill.
Accordingly, it is desirable to provide a simple and cost efficient system for distributing leads and associated medical activators from an IMD to one or more body locus. In addition, it is desirable to reduce the number of components associated with an IMD and thereby improve the reliability of the IMD and the associated system. It is further desirable to provide a system for non-invasively relocating an electrical field after the system is implanted. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.